Recently, interest in power generators using alternative energy is increasing because of the exhaustion of conventional fossil fuels and serious environment pollution.
Examples of the power generators using alternative energy include a nuclear power generator using nuclear energy, a solar power generator using solar energy, a wind power generator using wind energy, and a tidal power generator using tidal energy of sea water.
Among these power generators, the wind power generator and the tidal power generator convert a rotational force generated by winds and waves as power generation sources into power, respectively, and use a synchronous machine, specifically a permanent magnet synchronous machine.
In general, a plurality of wind power generators and tidal power generator are used to generate power. Since strength of winds and waves, which are power generation sources, are not constant, velocities of the power generation sources change continuously.
When the velocities of the power generation sources change continuously, powers generated by power generators have different amplitudes and phases, thus causing ripples.
As such, since an output power generated without consideration of each power generation amount has a ripple, the output power connected to an existing power network may make the power network unstable.
Even when the power generation amount is the same because each power generator generates power at the same velocity, an output power may have a ripple due to change in phase.
In a related art, in order to overcome these limitations, an energy storage device is used at an output end of a power generator to output a constant power.
However, the power generator using the energy storage device has a limitation in that the energy storage device leads to increase in a product cost.
In addition, in the related art, a method of changing a blade angle of a power generator according to a velocity of a power generation sources is used.
That is, the method of changing a blade angle of a power generator may include changing the blade angle to rotate the power generator slower when the velocity is high and faster when the velocity is low, thereby reducing the ripple.
However, the method of changing a blade angle of a power generator has a limitation in that its reliability is low because it is difficult to cope with a case in which the velocity changes quickly.